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Thread: Case fan splitter dilemma

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    Case fan splitter dilemma

    Hi, I've got a motherboard which only has one system fan header but I need to connect 2 case fans up which I can do using as case fan splitter. However the 2 case fans are different. Both are 80mm and are 12V fans but they differ in other ways. That is the rpm speeds are a bit different, one runs at between 1300 - 1800 rpm, the other runs at between 900 - 1750 rpms. They also have different amp requirements. One at 0.06 amps and the other at 0.09 amps.

    My question is will this potentially cause problems and has anyone done this before?

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    Banhammer in peace PeterB kalniel's Avatar
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    Re: Case fan splitter dilemma

    If you supply power to them at the right voltage they will draw the current (amps) that they need. As long as you can supply enough amps for both off the same header you are fine.

    You can also power one or more fans directly from the PSU using a molex-fan adaptor cable.

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    Treasure Hunter extraordinaire herulach's Avatar
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    Re: Case fan splitter dilemma

    You'll also get voltage control, although RPM monitoring will only be connected on one header. Basically it will be fine.

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    Re: Case fan splitter dilemma

    Fan controller + Loads of fans FTW!!

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    Re: Case fan splitter dilemma

    Ok guys I tried connecting the 2 fans with a case fan splitter cable into the system fan header. The problem is only 1 fan is spinning so I don't think it works unless I've done something wrong.

    Any ideas?

    If I can't get it to work I'll just go with kalniel's suggestion.

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    Banhammer in peace PeterB kalniel's Avatar
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    Re: Case fan splitter dilemma

    Quote Originally Posted by theNewGuy View Post
    Ok guys I tried connecting the 2 fans with a case fan splitter cable into the system fan header. The problem is only 1 fan is spinning so I don't think it works unless I've done something wrong.

    Any ideas?

    If I can't get it to work I'll just go with kalniel's suggestion.
    If the fans are both fully working on their own then either the splitter isn't working, or the motherboard isn't supplying enough amperage through the header.

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    Re: Case fan splitter dilemma

    How much amperage does the header supply?

    I read somewhere that most headers supply one amp but am not sure.

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    Banhammer in peace PeterB kalniel's Avatar
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    Re: Case fan splitter dilemma

    Quote Originally Posted by theNewGuy View Post
    How much amperage does the header supply?
    I don't know. Check your manual or ask the manufacturer. 1A should be more than enough for two fans, though maybe they need more to start up?
    Last edited by kalniel; 02-04-2014 at 10:35 AM.

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    Re: Case fan splitter dilemma

    kalniel - it is indeed 1A on the system fan header.

    Not sure what the problems is but I have read on other forums that it is not a good idea to use a splitter cable with fans of different types. Ideally the fans should be the same in terms of RPM and amps so maybe that is the issue.

    Anyway I've now decided not to use the splitter cable for both fans. One of the fans is a Silverstone tek suscool 81 fan which came with a molex to 3 pin adaptor to plug into the power supply so I'm just using that for that particular fan. It's working great.

    The other fan is a noctua NF-R8 which came with such a short cable that it doesn't even reach the system fan header without using some kind of extension. So basically I've had to use the splitter cable and plug that in to hook it up to the fan. I have noticed one thing about this fan and that is when I turn the computer on it spins up then stops. Sometimes it does not start to spin up again until windows loads up. Is this normal?

    Also it doesn't seem to be picked up on cpuid HWMonitor even though I can see it spinning.

    One last thing because of the situation with the noctua fan I'm considering just connecting both fans to the power supply rather than to the system fan header so could anyone recommend any molex-fan adaptor cables. Please bear in mind that the Silverstone suscool 81 fan is only a 3 pin fan and the noctua fan is a 4 pin fan.

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    The late but legendary peterb - Onward and Upward peterb's Avatar
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    Re: Case fan splitter dilemma

    If the fan current at 12 volts is as you say, the combined current is (from the figures you supplies) is 150mA, which I would have thought is well within the capabilities of the fan header. However, if the fans are three pin, then the third wire is usually a speed sense, and the mono won't be able to determine which fan is which, you will only be able to sense the speed of one fan.

    A four pin fan uses the fourth pin for Pulse Width Modulation speed control, so trying to drive a three pin and a four pin fan from a four pin header is unlikely to be successful with a simple splitter.

    The four pin fan should go to the mono header and connect the other to the psu via an adapter. It will fun at full speed, and you won't get any information back from it. Some fans provide a cable with a resistor in series with the supply lead. This limits the current taken by the fan, and reduces the speed. It is also possible to modify the fan adapter so the fan gets a seven volt supply from the psu, which also reduces the speed, but don't do this unless you are confident about making modifications.

    The main reason for reducing fan speed is to reduce the noise, so unless that is a problem, just run the auxiliary fan (connected to the PSU) at full speed.
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    Re: Case fan splitter dilemma

    That's the solution I've taken peterb and everything is working fine. However the noctua NF-R8 does seem to take a while to start up. I'm really not sure if it's because the fan is designed to not run unless it needs to or if there is something wrong. It's never failed to start spinning but sometimes I'm in windows for a few minutes before I can see the fan start to spin.

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    Re: Case fan splitter dilemma

    If it is connected to the mono header, it will run when the motherboard temperature reaches a certain threshold. That threshold is usually adjustable in the BIOS set up..
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    Re: Case fan splitter dilemma

    That's good to know peterb. As for setting the threshold in the bios, it doesn't seem possible. The options for this motherboard(Gigabyte h55m-ud2h) are extremely limited. Only the cpu fan can be set and the only options are auto, voltage or PWM. There are no settings available for the system fan.

    The only reason I'm a bit hesitant about all of this is because the noctua fan is the one above the graphics card and I need to be certain that the fan is working without fault.

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